/* -------------------------------------------------------------------------
 *
 * kwlookup.cpp
 *	  lexical token lookup for key words in openGauss
 *
 * NB - this file is also used by ECPG and several frontend programs in
 * src/bin/ including pg_dump and psql
 *
 * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *	  src/common/backend/parser/kwlookup.cpp
 *
 * -------------------------------------------------------------------------
 */

/* use c.h so this can be built as either frontend or backend */
#include "c.h"

#include <ctype.h>

#include "plugin_parser/keywords.h"

/*
 * ScanKeywordLookup - see if a given word is a keyword
 *
 * Returns a pointer to the ScanKeyword table entry, or NULL if no match.
 *
 * The match is done case-insensitively.  Note that we deliberately use a
 * dumbed-down case conversion that will only translate 'A'-'Z' into 'a'-'z',
 * even if we are in a locale where tolower() would produce more or different
 * translations.  This is to conform to the SQL99 spec, which says that
 * keywords are to be matched in this way even though non-keyword identifiers
 * receive a different case-normalization mapping.
 */
const ScanKeyword* ScanKeywordLookup(const char* text, const ScanKeyword* keywords, int num_keywords)
{
    int len, i;
    char word[NAMEDATALEN] = {0};
    const ScanKeyword* low = NULL;
    const ScanKeyword* high = NULL;

    if (text == NULL) {
        return NULL;
    }

    len = strlen(text);
    /* We assume all keywords are shorter than NAMEDATALEN. */
    if (len >= NAMEDATALEN) {
        return NULL;
    }

    /*
     * Apply an ASCII-only downcasing.	We must not use tolower() since it may
     * produce the wrong translation in some locales (eg, Turkish).
     */
    for (i = 0; i < len; i++) {
        char ch = text[i];

        if (ch >= 'A' && ch <= 'Z') {
            ch += 'a' - 'A';
        }
        word[i] = ch;
    }
    word[len] = '\0';

    /*
     * Now do a binary search using plain strcmp() comparison.
     */
    low = keywords;
    high = keywords + (num_keywords - 1);
    while (low <= high) {
        const ScanKeyword* middle = NULL;
        int difference;

        middle = low + (high - low) / 2;
        difference = strcmp(middle->name, word);
        if (difference == 0) {
            return middle;
        } else if (difference < 0) {
            low = middle + 1;
        } else {
            high = middle - 1;
        }
    }

    return NULL;
}
